This invention relates to a process for making an achromatic hologram which is adapted to be reconstructed with white light and which is recorded on a photographic record carrier by means of an object beam and a reference beam of coherent monochromatic light in an operation in which the object beam passes through an image-forming optical element between the object and the recording material.
Such a process is known, e.g., from U.S. Pat. Nos. 3,633,989 and 3,944,322.
In the process known from U.S. Pat. No. 3,633,989, a hologram is made which has only a horizontal axis so that it represents a stereoscopic image which is reproducible in a horizontal direction. As a result, the image has a relatively low information density because the information along the vertical axis is filtered out. Such image is suitable, e.g., for electronic transmission. This known prior process will be explained hereinafter in more detail with reference to FIGS. 1 to 3.
On the other hand, U.S. Pat. No. 3,944,322 discloses measures for improving the reproduction of such a hologram which can also be autostereoscopically reconstructed in achromatic form in one direction only.
Still further, the so-called open aperture process is known from the publication "Holography Handbook", Ross Books, P.O. Box 4340, Berkeley, Calif. 94704. This process will be explained hereinafter with reference to FIGS. 4 to 6.
In view of the known processes mentioned above, it is an object of the present invention to provide a process for making an achromatic hologram of improved quality with the aid of simpler means and which resulting hologram is adaptable to being autostereoscopically reproduced in all axial directions as well as adaptable to being mechanically duplicated by means of embossing.